The present invention relates to methods and devices for preventing or reducing a voltage-induced corrosion of a positive (anodic) contact. In particular the invention is related to anodic protection when both positive and negative contacts are immersed in a conductive solution.
Electrical devices often have positive and negative contacts or connectors to enable one device or component to be electrically connected to another device or component. When the negative and positive contacts are immersed in a conductive fluid, such as perspiration, a parallel circuit can be created between the negative and positive contacts which, over time, can cause anodic material to corrode and dissolve into the conductive solution and form a deposit over the negative (cathodic) contact.
One such instance where anodic corrosion can occur is with multi-component hearing devices, such as a behind-the-ear (BTE) hearing aid or a BTE component of a cochlear implant. A partially implantable cochlear implant system can have both an external BTE component and an implanted component. To overcome sensorineural deafness, numerous implantable cochlear stimulation (ICS) systems have been developed which bypass the hair cells in the cochlea and directly stimulate the auditory nerve fibers in order to induce the perception of sounds in the affected individual. The use of a cochlear implant to restore hearing to the profoundly deaf is now a well-accepted medical procedure.
BTE hearing aids and cochlear implants typically consist of two or more component parts which may be detachable. For example, one component of the BTE device can contain a battery. A second component of the BTE device can have processing circuitry for converting sound waves into electrical signals. The second component can have an integral or a separate, detachable earhook which permits the fully assembled external BTE device to hang over and behind the ear. The first component which contains the battery and the second, main component of the BTE can be electrically connected using positive and negative electrical contacts.
In the presence of a conductive fluid such as perspiration, a parallel circuit is created between the positive and negative contacts via the conductive fluid. In general, the parallel current flowing between the two contacts is very small and, in most instances, the intended electrical connection between the two components remains viable. Yet, over time, this parallel, parasitic flow of current can result in voltage-induced erosion, from corrosion of the positive contact (anode). The rate of erosion typically increases as the voltage potential between the anode and cathode is increased.
There are several known methods for preventing or reducing corrosion of an anodic material. The first method employs a passive anodic protection by placing a more anodic material close to a metal which is to be protected. A second method is anodic protection that is achieved by using a power supply to reverse the effects of galvanic corrosion. Neither method, however, provides adequate protection from voltage-induced erosion in the specific medical device applications described.
What is thus needed is a more effective device or method for preventing erosion of a positive (anodic) contact between external device components such as a multi-component BTE under DC bias.